They say that shit runs downhill. This is commonly understood to mean that the world is an unfair place, except among those few people who actually work with the substance, for whom it is considered something of an article of faith. This is because municipal sewerage systems are powered almost entirely by gravity, which means that when working properly, they move millions of gallons of sewage a day across considerable distances with only a minimum expenditure of energy, a feat of efficiency virtually unparalleled in the annals of engineering. When sewage stops running downhill, as it inevitably does from time to time, very bad things indeed can happen, as they did on Pecan Springs Road, in the Austin neighborhood known as Windsor Park, one morning last September.

I was spending the day with an Austin Water Utility emergency-response crew when dispatch got a call from a woman reporting that two rooms of her house were flooded with sewage. Our crew consisted of a TV truck, piloted by a twenty-year line-maintenance veteran named David Eller, and a flusher truck, driven by another longtime utility employee, named Dale Crocker. At the house, Eller, who wears wraparound sunglasses and looks a little like the country singer Dwight Yoakam, unspooled a thick red cable from the back of his truck. On the end of the cable was a camera about the size of a roll of quarters, which Crocker shoved down into a PVC clean-out pipe near the curb in the front yard. The woman leaned on a walker in her driveway, looking worried.

The pipe came into view on a screen mounted near the truck’s rear doors. The walls of the pipe were colored a pleasing aquamarine, and the inside looked remarkably clean as the camera moved slowly forward, scudding along through the trickle of water on the bottom of the pipe. After only a few feet, however, something white and fibrous appeared at the top of the screen. “Tree roots at three feet,” Eller announced.

Trees are the bane of all underground infrastructure, but they are particularly hard on wastewater systems. Tree roots end in tiny tendrils, which act as notoriously efficient water diviners, constantly probing and searching for moisture under the earth. If a pipe has even a pinhole leak, which often occurs at joints, the tree will find it and begin slowly working its way into the opening. Root tendrils no more rigid than a stalk of celery can penetrate concrete or iron, in a sort of slow-motion version of a tornado slamming a two-by-four through a car door. There is no way to stop this, though many ideas have come and gone, including pipelines that exude their own herbicide. Once inside a pipe, roots flourish in the moisture-rich environment, eventually forming dense root-balls through which solids cannot pass.

In this case, the culprit was almost certainly a fifty-foot cottonwood in the middle of the front yard. A few feet past the root-ball, Eller detected a wastewater-filled sag in the line, probably caused by roots from the same tree pressing down on the top of the pipe. The root-ball was the most likely cause of the clog, but a sagging pipe can spell trouble down the road for a property owner—or PO, as the line crews call them—if it gets worse and causes the line to break. Still, Eller assured me that the woman had gotten off easy. Clogs in sewer mains—the larger lines that run under the street collecting sewage from the smaller service laterals that connect to homes—can be much worse. If you happen to live just upstream of the spot where the main in your street is clogged, what backs up in your toilet is not just your own sewage but your neighbors’ too. Like all flooding victims, the lower you are in the topography of your neighborhood, the worse you get it. Eller recalled one emergency he went out on last year in East Austin. “This guy indicated to me that shit water was shooting out of his toilet with five hundred roaches coming out of it,” he said, outlining with his arms an imaginary column of brown water and roaches.

“Worst I ever saw was off of Salton Drive,” Eller continued. In that incident, a main had been completely eaten out by hydrogen sulfide, an acidic gas that collects in pipes that are not flowing well. Over time, hydrogen sulfide can turn concrete into a porridge-like mush. Another component of sewer gas, methane, can be poisonous to breathe at high-enough concentrations. Last July, a farmer in Virginia walked down into a holding pit of liquefied cow manure and hit an invisible pocket of methane so concentrated that he instantly dropped dead. When his wife and two daughters went down to retrieve him, they dropped dead too. On Salton Drive, the gas had been so potent that the main was simply gone. “Must have flooded sixteen homes,” Eller recalled. “I mean, it was a foot up on the sides of their houses. The street was just full of water, women’s products floatin’ everywhere. The POs were freakin’ out.”

A flusher truck carries an array of obstruction-busting nozzles, each designed for a different type of blockage and a different size of pipe. The larger ones are two feet long and weigh upward of thirty pounds. Crocker showed me his collection of smaller, service-lateral-size nozzles, stainless-steel implements of destruction that he kept in a padded case reminiscent of something Q would hand 007 in the first act of a Bond movie. For this job Crocker chose a Warthog, a shiny four-inch-long device shaped like a fifties pencil sharpener. The Warthog screws onto the end of a hose and spins around like crazy when you send water through it, cutting up roots and whatever else might get in its way. If it were not inside the pipe when you turned on the water, the Warthog would whip around like one of those front-yard water toys kids used to play with, except that